1. Field of the Invention
The present invention relates to a receiving device used for small area communication, represented by dedicated short range communication and wireless LAN communication, and a transmitting/receiving device, a transport apparatus and communication system including the receiving device.
2. Prior Art
FIG. 23 is a block diagram illustrating the configuration of known vehicle-mounted communication system used for dedicated short range communication and the like. The vehicle-mounted communication system of FIG. 23 includes a control section 171 including a CPU 172 and a signal processing circuit 173, a transmitter 174, a circulator 175 connected to an antenna 176, a receiver 177 and an oscillator 178. Moreover, a power supply circuit 179 for supplying a power supply voltage is connected to the signal processing circuit 173, the CPU 172, the receiver 177 and the oscillator 178. A power supply voltage is supplied to the transmitter 174 via a switch circuit (SW circuit) 180 (see, for example, Japanese Laid-Open Publication No. 2000-278201).
Next, the operation of the known vehicle-mounted communication system will be further described.
FIG. 24 is a diagram illustrating the operation of the known vehicle-mounted communication system. In an ETC (electric toll collection) system or the like, when a vehicle with a vehicle-mounted communication system is outside of a communication area of an antenna of a base station (roadside wireless equipment), a timer function of the CPU 172 is operated. When a predetermined time set in the timer has lapsed, the vehicle-mounted communication system is turned to a sleep mode. In the sleep mode, the CPU 172 and the oscillator 178 are stopped by control of the signal processing circuit 173. At the same time, the switch circuit 180 is turned OFF and a power supply to the transmitter 174 is stopped.
In this state, when the vehicle with a vehicle-mounted communication system approaches the communication area of the antenna of the base station (roadside wireless equipment) and the antenna 176 of the vehicle-mounted communication system receives a call data signal from the base station (roadside wireless equipment), in response to the data signal, the signal processing circuit 173, in response to the received data signal, operates the oscillator 178 and the CPU 172 and also turns ON the switch circuit 180 to make the transmitter 174 supply power. Thus, the vehicle-mounted communication system becomes in an active mode and capable of transmission to the base station.
When transmission to the base station has been completed, the vehicle-mounted communication system becomes in a halt mode. In the halt mode, while the oscillator 178 stays in an operation state, only operations of the CPU 172 and the transmitter 174 are stopped. When the vehicle-mounted communication system re-starts its operation, the oscillator 178 is in an operation and thus no waiting time is required to re-start an operation of the oscillator 178. Accordingly, the vehicle-mounted communication system can be returned to an active mode from a halt mode.
In the known example, a halt mode is set between a sleep mode and an active mode. Thus, power consumption in a non-communication state can be suppressed and also the vehicle-mounted communication system can quickly return to an active mode in response to a request for re-connection, so that a response speed with respect to a re-connection request can be increased.